Dozens of sailors were overcome by heat exhaustion when temperatures rose dramatically on board a British nuclear submarine after a “catastrophic” air-conditioning failure.

Eight submariners were left in a “life threatening condition” as temperatures on HMS Turbulent passed 140F (60C) with 100 per cent humidity.

The previously undisclosed incident in the Indian Ocean has come to light three years later, after the commanding officer at the time gave a dramatic account of the crisis, saying that the situation had been so bad that he thought crew members were going to die.

Ryan Ramsey said: “I genuinely thought there was going to be a loss of life on board. People were going to die.”

The 44-year-old, who recently retired from the Royal Navy after 25 years’ service, said the extreme temperatures left crew “just collapsing everywhere, many at their work stations”.

The hunter-killer submarine was only three hours from Fujairah in the United Arab Emirates on May 26, 2011, when the incident took place.

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The vessel had surfaced and Mr. Ramsey was on the bridge when engineers told him the air conditioning plants had “catastrophically” failed. As he went below he was met by an “incredible blast of heat,” and the first casualties soon began to be taken ill.

Within hours many areas of the 275ft submarine had become makeshift sick bays, as 26 crew were taken ill. “We had casualties in the control room, the engine room, the bridge, the wardroom, cabins, and the toilets and showers. It was absolutely terrifying, and I’m not afraid to say I was scared,” he said.

“Walking around the boat I saw true fear in my crew’s eyes … we simply did not know how we were going to get through it.”

It was the first time such a malfunction had been reported on a vessel of that type — and the crew did not understand the exact cause of the problem. The heat meant the crew could not reach the problem areas because the equipment was too hot to touch.

A decision was made that it was impossible to return to Fujairah with a “broken” nuclear submarine because of the political fallout. The crew opened two of the hatches to release some of the heat and put some of the casualties outside, but with temperatures on the surface reaching 42C there was little respite. A decision was made to dive to cooler water to reduce the heat.

“It was touch and go before we dived as to what might happen to us and the submarine,” Mr. Ramsey said. “We couldn’t do anything. I could have radioed for help but it would have taken hours for anyone to reach us. In that time people would have died.” Diving to below 200 metres, the temperatures began to drop and within 24 hours systems had returned to normal and the crew were recovering.

We couldn’t do anything. I could have radioed for help but it would have taken hours for anyone to reach us

Mr. Ramsey said the problem was later traced to blockages in the submarine’s inlet pipes caused by crustaceans.

He told the local newspaper Plymouth Herald: “There’s not a day that goes by that I do not think about what happened, the pain of seeing my crew like that.

“But when I think back to that time I quickly remember how fantastic they all were in dealing with the situation.”

HMS Turbulent, a Trafalgar Class submarine, was decommissioned in 2012 after a career spanning nearly 30 years.